Information about chemical structure is encoded by 1000 populations of olfactory sensory neurons, each of which projects to defined glomeruli in the olfactory bulb. Each glomerulus and associated olfactory bulb neurons are thought to be functional units in olfactory processing. Understanding the functional connections among neurons in the olfactory bulb is critical to understanding how the olfactory system works. While traditional anatomical techniques can reveal the structure of neuronal circuits, determining which nerve cells actually communicate with one another in a complex circuit is more challenging. The goal of this proposal is to develop an optogenetic approach to map functional circuits in the mouse olfactory bulb. Using gene targeting, we are expressing a light-activated channel in genetically-defined populations of neurons, allowing us to selectively activate glomeruli using light. Using this photostimulation-based approach, we are mapping the receptive fields of olfactory bulb neurons and determining whether neurons associated with a specific glomerulus are functionally similar. The research described here will allow us to address fundamental questions about sensory processing that are not possible to address using available techniques. The methods that we develop will also be useful map circuits in other parts of the mammalian brain. PUBLIC HEALTH RELEVANCE: We propose to apply novel optogenetic technologies to map neuronal circuits in the mammalian olfactory system using light. The research described here will allow us to address fundamental questions about sensory processing that were previously not possible to address using traditional techniques.